Field emission double-plane light source and method for making the same

ABSTRACT

A field emission double-plane light source includes a first anode, a second anode, and a cathode separately arranged between the first and second anodes. Each of the first and second anodes includes an anode substrate, an anode conductive layer formed on a surface of the anode substrate, and a fluorescent layer formed on the anode conductive layer. The cathode has a metallic based network with two opposite surfaces, each facing a respective one of the first and second anodes. Each of the surfaces of the network has a respective electron emission layer thereon facing a corresponding fluorescent layer of one of the first and second anodes. Each of the electron emission layers includes a glass matrix, and a plurality of carbon nanotubes, metallic conductive particles, and getter powders dispersed in the glass matrix. A method for making such field emission double-plane light source is also provided.

RELATED APPLICATIONS

This application is related to commonly-assigned applications entitled,“FIELD EMISSION PLANE LIGHT SOURCE AND METHOD FOR MAKING THE SAME”,filed ***(Atty. Docket No. US10305), “FIELD EMISSION LAMP AND METHOD FORMAKING THE SAME”, filed **** (Atty. Docket No. US10306), “FIELD EMISSIONLAMP AND METHOD FOR MAKING THE SAME”, filed **** (Atty. Docket No.US10307), and “FIELD EMISSION ELECTRON SOURCE AND METHOD FOR MAKING THESAME”, filed ***(Atty. Docket No. US10313), the contents of each ofwhich are hereby incorporated by reference thereto.

BACKGROUND

1. Technical Field

The invention relates generally to cold cathode luminescent fieldemission devices and, particularly, to a field emission double-planelight source employing a getter to exhaust unwanted gas from therein,thereby ensuring a high degree of vacuum. The invention also relates toa method for making a field emission double-plane light source.

2. Discussion of Related Art

Recently, with the development of various plane display technologies,field emission display (FED) technology has been paid more attention, aswell. FED technology potentially offers, e.g., higher brightness, lowerenergy consumption, broader visual angle, and higher contrast thanpossible with liquid crystal or plasma displays. FED technology could beutilized in many fields including, e.g., personal computers, mobilecommunications, flat screen display/televisions, etc. In the planedisplay technology, a single plane display is typically used to displayin a determined direction. However, for, e.g., traffic lights,information displays used in public, a display operating in two oppositedirections is required. For solving this problem, two single planedisplays are arranged in two opposite directions to display in the twodirections. However, this arrangement typically increases the cost anddecreases the reliability of the plane display.

In order to decrease the cost of the plane display displaying in twoopposite directions and improving the performance of the plane display,a field emission double-plane light source can be employed in a fieldemission display as a light source. A nanotube-based field emissiondouble-plane light source usually includes a pair of anodes and acathode arranged between the anodes. The cathode has a pair of electronemission layers on two opposite surfaces thereof, and each of theelectron emission layers has a plurality of the carbon nanotubesassociated therewith. The anodes each have a respective fluorescentlayer facing the corresponding electron emission layers of the cathode.In use, a strong electrical field is provided between the cathode andthe anodes, the field excites the carbon nanotubes of the cathode toemit electrons, and the electrons bombard the fluorescent layers of theanodes to thereby produce visible light in two opposite directions.

For a field emission double-plane light source, a high degree of vacuumwithin an inner portion (i.e., interior) thereof is a virtual necessity.In general, the better of the degree of vacuum of the field emissiondouble-plane light source that is able to be generated and maintainedwithin the field emission double-plane light source during the sealingprocess and/or thereafter during use, the better the field emissionperformance thereof is. To maintain the degree of vacuum of the fieldemission double-plane light source within a desired range, aconventional way is to provide a getter in the inner portion thereof.Such a getter is able to exhaust a gas produced by the fluorescent layerand/or any residual gas remaining within the field emission double-planelight source upon sealing and evacuation thereof. The getter isgenerally selected from a group consisting of non-evaporable getters andevaporable getters.

For the evaporable getter, a high temperature evaporating process has tobe provided during the fabrication of the field emission double-planelight source, and a plane arranged in the inner portion of the fieldemission plane source has to be provided to receive the evaporatedgetter. Thus, the cost of the fabrication of the field emissiondouble-plane light source increases, and the cathode and the anodes areprone to shorting during the high temperature evaporating process,thereby causing the failure of the field emission double-plane lightsource. For the non-evaporable getter, it is typically focused/providedon sidewalls of the field emission double-plane light source, and, thus,the degree of vacuum of portions away from the getter tends to bepoorer, in the short-term, than that of portions near to the getter, atleast until internal equilibrium can reached, thereby decreasing thefield emission performance of the field emission double-plane lightsource or at least potentially resulting in a fluctuating performancethereof.

What is needed, therefore, is a field emission double-plane light sourcethat overcomes the above-mentioned shortcomings to ensure a high degreeof vacuum thereof, thus providing a better and more steady fieldemission performance during the use thereof.

What is also needed is a method for making such a field emissiondouble-plane light source.

SUMMARY

A field emission double-plane light source generally includes a firstanode, a second anode, and a cathode. Each of the first and secondanodes includes an anode substrate, an anode conductive layer formed ona surface of the anode substrate, and a fluorescent layer formed on theanode conductive layer. The cathode is arranged between the first andsecond anodes and effectively separates the anodes from one another. Thecathode includes a conductive network with two opposite surfaces, eachfacing a respective one of the first and second anodes. Each of thesurfaces of the network has an electron emission layer facing acorresponding fluorescent layer of the first and second anodes. Each ofthe electron emission layers includes a glass matrix, and a certainnumber of carbon nanotubes, metallic conductive particles, and getterpowders dispersed in the glass matrix.

A method for making a field emission double-plane light source generallyincludes the steps of:

(a) providing a certain number of carbon nanotubes, metallic conductiveparticles, glass particles (later melted to form glass matrixes), andgetter powders; a conductive network; a pair of anodes (i.e., a firstanode and a second anode); and a number of supporting members, each ofthe anodes having an anode substrate, an anode conductive layer formedon the anode substrate, and a fluorescent layer formed on the anodeconductive layer;

(b) mixing the nanotubes, the metallic conductive particles, the glassparticles, and the getter powders in an organic medium to form anadmixture;

(c) forming layers of the admixture on an upper surface and a bottomsurface of the network;

(d) drying and then baking the admixture at a temperature of about 300°C. to about 600° C. to soften and/or melt the glass particles to resultin the glass matrix with the nanotubes, the metallic conductiveparticles, and the getter powders dispersed therein, in order to createelectron emission layers on the network and thus produce a cathode; and

(e) thereafter, assembling the anodes, the cathode and the supportingmembers, and sealing them and evacuating an interior defined by theanodes and the supporting members and thereby yielding the fieldemission double-plane light source.

Other advantages and novel features of the present field emissiondouble-plane light source and the related method of making such a lightsource will become more apparent from the following detailed descriptionof preferred embodiments, when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the present field emission double-plane light source andthe related method of producing such can be better understood withreference to the following drawings. The components in the drawings arenot necessarily to scale, the emphasis instead being placed upon clearlyillustrating the principles of the present field emission double-planelight source and the related method of producing such. Moreover, in thedrawings, like reference numerals designate corresponding partsthroughout the several views.

FIG. 1 is an isometric, disassembled view of a field emissiondouble-plane light source, in accordance with an exemplary embodiment ofthe present device;

FIG. 2 is an isometric view of the cathode shown in FIG. 1;

FIG. 3 is an isometric, assembled view of the field emissiondouble-plane light source of FIG. 1;

FIG. 4 is a cross-sectional view along a line IV-IV of FIG. 3; and

FIG. 5 is an enlarged view of a circled portion V of FIG. 4.

The exemplifications set out herein illustrate at least one preferredembodiment of the present field emission double-plane light source andthe related method of making such a light source, in one form, and suchexemplifications are not to be construed as limiting the scope of such afield emission double-plane light source and a method for making such inany manner.

DETAILED DESCRIPTION

Reference will now be made to the drawings to describe, in detail, thefield emission double-plane light source 10 and the method for makingthe same, according to the present embodiment.

Referring to FIG. 1, a field emission double-plane light source 10, inaccordance with an exemplary embodiment of the present device, isprovided. The field emission double-plane light source 10 includes afirst anode 20, a second anode 30, a cathode 40, a plurality ofsupporting members 50, and a sealing body 60. The cathode 40 is disposedbetween the first and second anodes 20, 30. The supporting members 50are disposed between the first anode 20, the cathode 40 and the secondanode 30 to separate/space the electrodes 20, 30, and 40 from oneanother. The sealing body 60 is formed around edges of the fieldemission double-plane light source 10.

The first and second anodes 20, 30 are arranged facing each other. Eachof the fist and second anodes 20, 30 includes an anode substrate 22, 32,an anode conductive layer 24, 34 directly formed, respectively, on acorresponding one of a bottom surface and an upper surface of the anodesubstrate 22, 32, and a fluorescent layer 26, 36 formed on the anodeconductive layer 24, 34, in contact therewith. The anode substrate 22,32 is beneficially a transparent glass or optical plastic plate. Theanode conductive layer 24, 34 is advantageously a transparent conductivefilm, such as an indium tin oxide (ITO) film. The fluorescent layer 26,36 is usefully made of at least one of white and color fluorescentmaterials. Such materials are opportunely chosen so as to have manysatisfactory characteristics (e.g., a high optical-electricaltransferring efficiency, a low voltage, a long afterglow luminescence,etc.). In an alternative mode, an aluminum film 28, 38 can be formeddirectly on a surface of the fluorescent layer 26, 36 in order toimprove the brightness of the field emission double-plane light source(due to both its electrical conductivity and reflectivity) and to helpreduce the opportunity of the fluorescent layer 26, 36 failingprematurely (e.g., from spalling).

Referring to FIGS. 2 to 4, the cathode 40 includes a conductive network42 (e.g., a metallic based network ) having securing edges 420. Thenetwork 42 has an upper surface (not labeled), facing the fluorescentlayer 26 of the first anode 20 and a bottom surface (not labeled),facing the fluorescent layer 36 of the second anode 30. The upper andbottom surfaces of the network 42 each have an electron emission layer44, 46 formed thereon. The network 42 is advantageously made of at leastone of a material selected from the group consisting of silver (Ag),copper (Cu), nickel (Ni), and gold (Au). The network 42 is preferablymade from Ni.

Referring to FIG. 5, each of the electron emission layers 44, 46includes a plurality of carbon nanotubes 440, 460, metallic conductiveparticles 444, 464, and getter powders 446, 466; and a glass matrix 442,462. The carbon nanotubes 440, 460, the metallic conductive particles444, 464, and the getter powders 446, 466 are dispersed in the glassmatrix 442, 462. A length of each of the nanotubes 440, 460 isadvantageously in the range from about 5 micrometers to about 15micrometers, a diameter thereof is usefully in the range from about 1nanometer to about 100 nanometers, and one end thereof is exposed out of(i.e., anchored within and extending therefrom) a top surface of theelectron emission layer 44, 46. The metallic conductive particles 444,464 are beneficially made of silver (Ag) or indium tin oxide (ITO) andare used to electrically connect the network 42 with the nanotubes 440,464. The getter powders 446, 466 are usefully made of a non-evaporatinggetter material (i.e., a material generally selected from the groupconsisting of titanium (Ti), zirconium (Zr), hafnium (Hf), thorium (Th),aluminum (Al), thulium (Tm), and alloys substantially composed of atleast two such metals). The average diameter of the getter powders 446,466 is advantageously in the range from about 1 micrometer to about 10micrometers.

Each of the supporting members 50 is advantageously made of atransparent and hard material, in order to protect the field emissiondouble-plane light source 10 from the atmospheric pressure thereon andfrom other exterior effects (e.g., potential environmental contaminationor mechanical impact), thereby ensuring the safety thereof. Preferably,the field emission double-plane light source 10 has four supportingmembers 50: a first two respectively arranged between the first anode 20and the cathode 40 on opposite sides of the cathode 40; and a second tworespectively arranged between the cathode 40 and the second anode 30 anddisposed on two opposite sides of the cathode 40.

The sealing body 60 is made from a sealing material (e.g., glass) toseal the edges of the field emission double-plane light source 10 tothereby form a sealed chamber in an inner portion thereof. Upon formingof such a sealed chamber, it is possible for the interior of the fieldemission double-plane light source 10 to be evacuated (so long as anevacuation/gas flow port remains that can be later sealed; otherwise,evacuation needs to occur prior to completion of sealing), achieving avacuum therein.

In use, a strong electrical field is provided for the first and secondanodes 20, 30 and the cathode 40. The strong field excites the carbonnanotubes 440, 460 of the electron emission layers 44, 46 to emitelectrons. The electrons bombard the respective fluorescent layers 26,36 of the anodes 20, 30, thereby producing visible light in two oppositedirections. Furthermore, the getter powders 446, 466 exhaust the gasproduced by the fluorescent layers 26, 36 and/or any potential residualgas in the field emission double-plane light source 10, thus ensuringthat the field emission double-plane light source 10 is able to maintaina high degree of vacuum.

A method for making the above-mentioned field emission double-planelight source 10 generally includes:

(a) providing a certain number of carbon nanotubes 440, 460, metallicconductive particles 444, 464, glass particles (later melted to formglass matrixes 442, 462), and getter powders 446, 466; a conductivenetwork 42; a pair of anodes 20, 30 (i.e., a first anode 20 and a secondanode 30); and a number of supporting members 50, each of the anodes 20,30 having an anode substrate 22, 32, an anode conductive layer 24, 34formed on the anode substrate 22, 32, and a fluorescent layer 26, 36formed on the anode conductive layer 24, 34;

(b) mixing the nanotubes 440, 460, the metallic conductive particles444, 464, the glass particles and the getter powders 446, 466 in anorganic medium to form an admixture;

(c) forming layers of the admixture on an upper surface and a bottomsurface of the network 42;

(d) drying and then baking the admixture at a temperature of about 300°C. to about 600° C. to soften and/or melt the glass particles to resultin the glass matrix 442, 462 with the nanotubes 440, 460, the metallicconductive particles 444, 464 and the getter powders 446, 466 dispersedtherein, in order to yield electron emission layers 44, 46 on thenetwork 42 to finally form a cathode 40; and

(e) thereafter, assembling and sealing the anodes 20, 30, the cathode40, and the supporting members 50 to define an enclosed interior, andevacuating the enclosed interior to yield the field emissiondouble-plane light source 10.

In step (a), the carbon nanotubes 440, 460 are formed by an appropriatetechnology (e.g., a chemical vapor deposition (CVD) method, anarc-discharge method, a laser ablation method, a gas phase combustionsynthesis method, etc.). Preferably, the average length of the nanotubes440, 460 is in the range from about 5 micrometers to about 15micrometers. The glass particles are selected from glass powders with alow melting temperature (e.g., glass powders with a low meltingtemperature in the range of about 350° C. to about 600° C., andpreferably composed, in part, of silicon oxide (SiO₂), boric trioxide(B₂O₃), zinc oxide (ZnO), and vanadium pentoxide (V₂O₅)). The averagediameter of the glass particles is preferably in the range of about 10nanometers to about 100 nanometers. The metallic conductive particles444, 464 are ball-milled, yielding particle diameters in the range fromabout 0.1 micrometer to about 10 micrometers. The getter powders 446,466 are also ball-milled, producing powder diameters in the range fromabout 1 micrometer to about 10 micrometers. Preferably, the getterpowders 446, 466 are made of a getter material with an activitytemperature of about 300° C. to about 500° C. (e.g., an alloy containingZr and Al). Each of the anode conductive layer 24, 34 is formed on thesubstrate 22, 32 by, e.g., a sputtering method or a thermal evaporatingmethod, and the fluorescent layer 26, 36 is created on the anodeconductive layer 24, 34 by, for example, a depositing method.

In step (b), the organic medium is composed of a certain amount ofsolvent (e.g., terpineol, etc.), and a smaller amount of a plasticizer(e.g., dimethyl phthalate, etc.) and a stabilizer (e.g., ethylcellulose, etc.). The percent by mass of the getter powders 316 is inthe range of about 40% to about 80% of the admixture. The process of themixing is preferably performed at a temperature of about 60° C. to about80° C. for a sufficient period of time (e.g., about 3 hours to about 5hours). Furthermore, low-power ultrasound is preferably applied in step(b), to improve the dispersion of the carbon nanotubes 440, 460, themetallic conductive particles 444, 464 and the getter powders 446, 466.

Step (c) is performed in a condition of a low dust content (e.g., beingpreferably lower than 1000 mg/m³).

In step (d), the process of drying volatilizes the organic medium fromthe network 42, and the process of baking melts or at least softens theglass particles to permit flow thereof in order to form the glassmatrixes 442, 462 of the electron emission layers 44, 46. The processesof drying and baking are performed in a vacuum condition and/or in aflow of a protective/inert gas (e.g., noble gas, nitrogen). An outersurface of each of the electron emission layers 44, 46 is advantageouslyabraded and/or selectively etched, in order to expose ends of at least aportion of the nanotubes 440, 460. The exposure of such ends increasesthe field emission performance of the electron emission layers 44, 46.

In step (e), a sealing material (e.g., a glass with a meltingtemperature of about 350° C. to about 600° C.) is applied so as toextend between and contact edges of both the first and second anodes 20,30 and the cathode 40 of the field emission double-plane light source 10and is softened/formed at a temperature of about 400° C. to about 500°C. The sealing material forms the sealing body 60 after cooling, toestablish a chamber within the field emission double-plane light source10 that can be evacuated. The sealing body 60, additionally, promotesthe mechanical integrity of the field emission double-plane light source10, helping to space the first anode 20 from the cathode 40 and spacethe second anode 30 from the cathode 40.

Finally, it is to be understood that the above-described embodiments areintended to illustrate rather than limit the invention. Variations maybe made to the embodiments without departing from the spirit of theinvention as claimed. The above-described embodiments illustrate thescope of the invention but do not restrict the scope of the invention.

1. A field emission double-plane light source comprising: a first anode;a second anode, each of the first and second anodes comprising an anodesubstrate, an anode conductive layer, and a fluorescent layer, the anodeconductive layer being formed on a surface of the anode substrate, thefluorescent layer being created on the anode conductive layer; and acathode arranged between the first and second anodes and separatedtherebetween, the cathode comprising a conductive network, the networkhaving two opposite surfaces each facing a respective one of the firstand second anodes, each of the surfaces of the network having anelectron emission layer thereon, each electron emission layerrespectively facing a corresponding fluorescent layer of one of thefirst and second anodes, each of the electron emission layers comprisinga glass matrix, and a plurality of carbon nanotubes, metallic conductiveparticles, and getter powders dispersed in the glass matrix.
 2. Thefield emission double-plane light source as described in claim 1,wherein the getter powders are composed of a non-evaporating gettermaterial.
 3. The field emission double-plane light source as describedin claim 1, wherein an average diameter of the getter powders is in therange from about 1 micrometer to about 10 micrometers.
 4. The fieldemission double-plane light source as described in claim 1, wherein thegetter powders are comprised of at least one a material selected fromthe group consisting of titanium, zirconium, hafnium, thorium, aluminum,and thulium.
 5. The field emission double-plane light source asdescribed in claim 1, wherein an average diameter of the nanotubes is inthe range from about 1 nanometer to about 100 nanometers, and an averagelength thereof is in the range from about 5 micrometers to about 15micrometers.
 6. The field emission double-plane light source asdescribed in claim 1, wherein the anode conductive layers of the firstand second anodes are each an indium tin oxide film.
 7. The fieldemission double-plane light source as described in claim 1, wherein themetallic conductive particles are comprised of a material selected fromindium tin oxide and silver, and an average diameter thereof is in therange of about 0.1 micrometer to about 10 micrometers.
 8. The fieldemission double-plane light source as described in claim 1, wherein theanode substrates of the first and second anodes are each a transparentglass plate.
 9. The field emission double-plane light source asdescribed in claim 1, wherein the network is comprised of a materialselected from the group consisting of silver, copper, nickel, gold andan alloy composed of at least two such metals.
 10. A method for making afield emission double-plane light source comprising: (a) providing aplurality of carbon nanotubes, metallic conductive particles, glassparticles and getter powders; a metallic based network; a pair ofanodes; and a plurality of supporting members, each of the anodescomprising an anode conductive layer and a fluorescent layer formed onthe anode conductive layer; (b) mixing the nanotubes, the metallicconductive particles, the glass particles, and the getter powders in anorganic medium to form an admixture; (c) forming layers of the admixtureon, respectively, an upper surface and a bottom surface of the network;(d) drying and baking the admixture at a temperature of about 300° C. toabout 600° C. to at least one of soften and melt the glass particles toresult in glass matrixes on the upper surface and the bottom surface ofthe network, thereby yielding a cathode; and (e) thereafter, assemblingand sealing the anodes, the cathode, and the supporting members togetherto obtain the field emission double-plane light source.
 11. The methodfor making the field emission double-plane light source as described inclaim 10, wherein the getter powders are comprised of a non-evaporatinggetter material having an activity temperature of about 300° C. to about500° C.
 12. The method for making the field emission double-plane lightsource as described in claim 10, wherein an average diameter of theglass particles is in the range from about 10 nanometers to about 100nanometers, and the melting temperature thereof is in the range fromabout 350° C. to about 600° C.
 13. The method for making the fieldemission double-plane light source as described in claim 10, wherein thepercent by mass of the getter powders is in the range of about 40% toabout 80% of the admixture.
 14. The method for making the field emissiondouble-plane light source as described in claim 10, wherein the processof mixing the nanotubes, the getter powders, the glass particles, andthe metallic conductive particles is performed at a temperature of about60° C. to about 80° C. for a time of about 3 hours to about 5 hours. 15.The method for making the field emission double-plane light source asdescribed in claim 10, wherein the drying and baking processes areperformed at least one of in a vacuum condition and under a flow of aninert gas.
 16. The method for making the field emission double-planelight source as described in claim 10, wherein after forming theelectron emission layers, outer surfaces of the electron emission layersare at least one abraded and etched in order to expose ends of thenanotubes.
 17. The method for making the field emission double-planelight source as described in claim 10, wherein during a step of sealingthe anodes and the cathode, a sealing material is applied between edgesthereof and heated up to a temperature of about 400° C. to about 500° C.to effect the sealing.